The invention concerns a device for checking the closed state of a door mounted on an object, in particular on a motor vehicle, by means of an electronic key with an optical display, wherein the object and the electronic key respectively have a transmitter and a receiver that intercommunicate within a defined spatial region.
Particular attention has been paid in recent years to protecting motor vehicles against break-in and theft. It has been contemplated to provide motor vehicles with preferably electronic security systems, which are designed to prevent access to a motor vehicle by unauthorized persons or to make this more difficult. For this, motor vehicles are equipped with electronic theft protection devices, vehicle immobilization systems and alarm systems. Electronic systems of this type frequently have electronic displays in the form of light-emitting diodes, which light up when the system is "alarmed" and which indicate whether an alarm system, theft protection device or vehicle immobilization system is activated.
Particular attention is paid to the doors as access elements of the motor vehicle. Increasingly, doors are provided with electronic locks that can be operated with an electronic key, preferably a remote control. The doors generally can be opened and closed only by the owner of the electronic key.
An electronic key designed as remote control is known, which unlocks the doors of a motor vehicle upon activation of a button. When leaving the motor vehicle, all doors of the motor vehicle can be locked by pushing another button. The doors have closure detecting sensors that intercommunicate with a receiver located inside the motor vehicle. If the user of the motor vehicle wants to check whether all doors of the motor vehicle are closed, then he/she can activate the door-locking button on the electronic key again within a spatially limited range. If all doors are closed, then the receiver unit installed inside the motor vehicle emits an impulse to an acoustic signaling device, the motor vehicle horn, which then confirms the closed state of the door with a short acoustic beep. If one of the doors is not closed, no acoustic signal is emitted. One particular disadvantage of this device is that this acoustic signal sound as a rule is viewed as disrupting to the environment, in particular at night or in parking garages. In an acoustically noisy environment, the acoustic signal frequently cannot be assigned to the respective motor vehicle. Finally, an acoustic sound is not suited to continuously indicate the "closed" state of the motor vehicle. A reassurance as to whether the doors of the motor vehicle are actually locked can be gained only through repeated activation of the locking button on the electronic key, wherein it is not possible to visually observe the locked state of the door.
In accordance with the GB-A-2 240 418, a remote control for motor vehicle doors essentially comprises a portable remote control unit and a control unit arranged inside the motor vehicle. Each of these units has a transmitter and a receiver, which intercommunicate within a defined spatial region, so that an exchange of information occurs, which signals the closed state of the door mounted on the motor vehicle. A display means mounted on the remote control unit visually displays whether the motor vehicle door is closed or not.
A similar locking arrangement for one or several lockable covers over motor vehicle openings is disclosed in the DE-U-91 11 651. The locking arrangement comprises a hand-held transmitter with receiver, as well as respectively one receiver and one transmitter arranged in the motor vehicle, which intercommunicate. A lock installed on a cover for the motor vehicle is connected to a sensor in a way that is not elaborated upon, which sensor detects the closed state of the lock and transmits a corresponding signal to a control unit arranged in the motor vehicle. This control unit pulses the associated transmitter, which then transmits a signal to the hand-held transmitter/receiver unit.
An optical display of an alarm system in a motor vehicle also shows only whether or not the alarm system is operational. However, it does not show whether the doors are open or closed.